Mammalian spermatogenesis is a hormone-dependent process regulated mainly by follicle-stimulating hormone (FSH) and testosterone (T). The effects of these hormones on germ cell (Gc) differentiation are believed to be indirect, mediated through the somatic Sertoli cells (Sc). Although T and/or FSH were shown to affect various Sc functions, including the secretion of many proteins (i.e., androgen binding protein, inhibin, transferrin, plasminogen activator), the mechanism by which the Sc mediates the hormonal effects on the Gc is not known. The overall objective of this proposal is to clarify the Sc-Gc interaction by further exploring a hypothesis that certain products which may be required by the Gc, are produced by the Sc and are transferred to the Gc during certain stages of their differentiation. The specific aims are: 1) to investigate the uptake of some prelabeled Sc products (peptides, proteins, glycoproteins and RNA) by the Gc at specific stages of differentiation, by using radioautography and isotope counting methods. During the initial grant period, we obtained evidence for high affinity, specific binding of androgen binding protein to the pachytene spermatocytes, and binding of transferrin to both pachytene spermatocytes and round spermatids, suggesting that some Sc products may be transferred to the Gc by a receptor-mediated mechanism; 2) to explore the effects of FSH and T on the secretion and transfer of the Sc products; 3) to identify the chemical nature of the transferred Sc products, not yet characterized, by using various immunologic (RIA, immunoprecipitation, immunofluorescence) and biochemical (two-dimensional gel electrophoresis, Western blots, HPLC, etc.) methods; 4) to examine if there is a correlation between the transfer of specific Sc products and Gc differentiation. These studies should provide additional information on the mechanism by which hormones regulate spermatogenesis and on the role of Sertoli cells in this process.